Glycoproteins of cell surfaces apparently have an important role in antigenecity, cell growth, and cytodifferentiation and cellular recognition. The objectives of the present study are to elucidate the biochemical, immunochemical, and structural properties of intact membrane glycoproteins, especially those of the plasma membrane, from both normal and neoplastic cells. Presently, we are studying the enzyme nicotinamide adenine dinucleotide glycohydrolase (E.C. 3,2.2.5.) which has a high specific activity in the plasma membrane fraction obtained from rat liver homogenates.